Synthetic industrial oils made with &#34;tri-synthetic&#34; base stocks

ABSTRACT

This invention describes a blend of three base stock fluids, a PAO, an alkylated aromatic and a aromatic ester that synergistically improve the solvency for industrial lubricant additives such as oxidation and rust inhibitors, extreme-pressure/antiwear agents, metal deactivators and the like. The blend also has excellent hydrolytic stability plus improved dispersancy and resistance to deposit formation without degrading demulsibility.

FIELD OF INVENTION

[0001] The present invention relates to lubricant base stock blends.More particularly, the present invention is directed toward base stockshaving unexpectedly improved resistance to deposit formation, improvedsolubility for lubricant additives, degradation products and enhanceddemulsibility.

BACKGROUND OF INVENTION

[0002] Synthetic lubricant base stocks prepared by oligomerizing one ormore alpha olefins are well known commercially available materials thathave low pour points and high viscosity indices. Lube products employingthese poly-alpha-olefins (PAO's) typically are combined with a morepolar co-base stock such as alkylated aromatic fluids or polyol estersor certain dispersant additives such as polyalkylene type additives.

[0003] The inclusion of alkylated aromatic base fluids such as alkylatednaphthalene in PAO base fluids provides the fluid blend with improvedhydrolytic stability but there remains a need to provide the blend withimproved dispersancy.

[0004] The inclusion of polyalkylene type additives in PAO base fluidsprovides enhanced dispersancy but these additives form stable emulsionswith water and degrade the hydrolytic stability of compositionsemploying them thereby limiting the use of the blend to applicationswhere water ingress is not a problem.

[0005] The inclusion of polyol esters in PAO base fluids provides gooddispersancy but poor hydrolytic stability.

[0006] Therefore, one object of the present invention is to provide alubricant product of improved dispersancy along with good demulsibilityand hydrolytic stability.

SUMMARY OF INVENTION

[0007] Briefly stated the present invention is a synergistic combinationof synthetic fluids useful as lubricant base stock blend and comprisingabout 10 wt % or more of a PAO fluid; about 1 wt % or more of analkylated aromatic fluid and about 1 wt % or more of an aromatic ester.

[0008] In a preferred embodiment the lubricant base stock comprises:

[0009] from about 10 wt % to about 98 wt % of a PAO fluid;

[0010] from about 1 wt % to about 59 wt % of an alkylated aromatic; and

[0011] from about 1 wt % to about 75 wt % of an aromatic ester,

[0012] all amounts based on the weight of the blend.

[0013] Advantageous features of the invention will become apparent fromthe detailed description that follows.

BRIEF DESCRIPTION OF DRAWINGS

[0014]FIG. 1 is a graphic comparison of the storage stability of acommercial lubricant composition with one using a base stock of theinvention.

[0015]FIG. 2 graphically illustrates the deposit control property of abase stock of the invention.

[0016]FIG. 3 graphically compares the water demulsibility of acommercial composition with one using a base stock of the invention.

[0017]FIG. 4 graphically compares the oxidative and hydrolytic stabilityof two base stocks formulations of the invention with two others.

DETAILED DESCRIPTION OF INVENTION

[0018] Applicant has discovered that a blend of three lubricant fluids,viz a PAO, an alkylated aromatic and an aromatic ester has improvedsolvency for lube additives such as oxidation and rust inhibitors, metalpassivators and the like. The blend also has improved hydrolyticstability, dispersancy and resistance to deposit formation withoutdegrading demulsibility making the blend useful in a wide range ofindustrial applications. Indeed, fully formulated lubricant compositionsemploying the base stock of the present invention are especiallysuitable for use in applications where there is the potential for waterof moisture ingress such as oils used in combined cycle turbines, papermachinery, rod mills and the like.

[0019] The blended base stock of the invention includes at least about10 wt % of a PAO fluid. In general, the blend will comprise from about10 wt % to about 98 wt % of the PAO fluid, based on the total weight ofthe blend. Preferably, the blend will comprise from 60 wt % to 95 wt %,and more preferably from 80 wt % to 85 wt %.

[0020] PAO fluids and their preparation are well known in the art. ThosePAO's suitable in the practice of the present invention may be derivedfrom C₂ to about C₃₂ alpha olefins with C₈ to about C₁₆ alpha olefinsbeing preferred. Typically the PAO will have a viscosity in the range ofabout 3 cSt to about 300 cSt at 100° C. The preferred PAO a viscositywill, of course, depend upon factors such as the nature and amount ofthe other components used in the blend and the intended end use for thelubricant base stock blend.

[0021] The base stock blend of the present invention also includes aalkylated aromatic compound such as alkylated benzene, naphthalene,anthracene, biphenyl and the like. Like the PAO's, alkylated aromaticsand their method of preparation are well known in the art. Suitablealkylated aromatics are those having one or more short chain alkylgroups of from 1 to about 8 carbon atoms. The preferred alkyl aromaticswill have viscosities in the range of about 3 cSt to about 300 cSt at100° C. The alkylated aromatics will comprise about 1 to about 59 wt %of the total blend, preferably about 5 wt % to about 35 wt % and morepreferably about 10 wt %.

[0022] The base stock of the present invention also includes an aromaticester fluid. Common lubricant grade aromatic esters such as phthalateesters, mono- and diesters, polyol ester and ester with tails contain S,N and O suitable in the blend of this invention are commercial availablematerials typically formed by reacting an organic acid or anhydride withstraight or branched alcohols. Such esters have viscosities in the rangeof about 4 cSt to about 30 cSt at 100° C. In general, the amount ofaromatic ester employed in the base stock blend will be about 1 wt % toabout 75 wt %, and preferably from about 2 wt % to about 25 wt % of thetotal blend, with about 5 wt % to 8 wt % being more preferred.

[0023] An advantageous feature of the base stock blend of the presentinvention is its ability to solubilize additives such as heterocyclicrust inhibitors, antioxidants, antiwear agents, corrosion inhibitors andthe like. Among the antioxidants suitable for use in the base stockblend specific mention is made of aminic and phenolic type antioxidants.Suitable antiwear agents include alkylated triphenyl phosphates,phosphorophites, diorganodithiocarbamates and the like.

[0024] The following examples and comparative examples furtherillustrate the many advantageous of the instant invention.

EXAMPLES Example 1

[0025] A base stock according to the present invention comprising 84 wt% of a PAO (6 cSt at 100° C.) 10 wt % of an alkyl aromatic (alkylatednaphthalene) fluid (5 cSt at 100° C.) and 6 wt % of an ester fluid(diisooctylphthalate) was used in preparing a fully formulated lubricantcomposition (Formulation A) by blending the base stock with thefollowing additives:

[0026] (1) 0.4 wt % hindered phenolic and diphenyl amine typeantioxidants and 1:1 ratio;

[0027] (2) 1.5 wt % butylated triphenyl phosphate type antiwear agent;and

[0028] (3) 0.1 wt % of an ashless rust inhibitor.

[0029] The composition was maintained at 100° C. for 16 weeks withoutany evidence of haze or floc. Haze or floc, of course, is indicative ofadditive insolubility.

[0030] In contrast, a commercially available composition comprising a 6cSt at 100° C. PAO, 20 wt % diisodecylphthalate ester and substantiallythe same amounts of similar type additives of Formulation A after sixweeks displayed a trace of haze and moderate floccing.

[0031]FIG. 1 graphically presents the results of the tests andillustrates the improved solubility that the base stock of the inventionhas for lubricant additives.

Example 2

[0032] The deposit control of the base stock of the invention wascompared to a commercially available lubricant composition (Comparative2) by subjecting Formulation A of Example 1 and Comparative 2 to theCincinnati Machine Thermal Test A. The Comparative 2 composition has aPAO base fluid, typical additives and 1.0 wt % of a dispersant. Theresults of the text are graphically shown in FIG. 2. As can be seenunder the text conditions Formulation A exhibited excellent low depositformation. Moreover, when the test was modified by raising the testtemperature from 275° F. to 350° F. at the end of 168 hours visualinspection of the samples showed that the Formulation A had far lessdeposit formation.

Example 3

[0033] Formulation A of Example 1 and a commercial lubricant composition(Comparative 3) were subjected to the ASTM-D 1401 demulsibility test.Comparative 3 was a PAO based lubricant containing 1.0 wt % of apolyalkylene dispersant. The results of the tests are shown in FIG. 3.

[0034] As can be seen, Formulation A with the base stock of theinvention showed complete water separation within 10 minutes.Formulation A, of course, did not contain a demulsfier additive.

Example 4

[0035] This example compares the oxidative and hydroytic stability, asdetermined by ASTM D 943 TOST life test, of two base stocks of theinvention (A and B) with two other base stock (C and D). Base stock Acomprised 80 wt % PAO (6 cSt at 100° C.); 10 wt % of an alkylatednaphthalene (5 cSt at 100° C.) and 6 wt % an ester fluid(diisooctylphthalate). Base stock B differed from A in that the esterwas a 50:50 mixture of ditridicyl phthalate and terephtalate ester.

[0036] Base stock C and D used the same PAO as A and B. The alkylatedaromatic fluid of C was the same as in A and B while the ester of D wasa trimellitatte ester.

[0037] The results of the tests are shown in FIG. 4.

[0038] As can be seen A and B display 30% longer life than C.

What is claimed is:
 1. A lubricant base stock blend comprising: about 10wt % or more of a polyalpha olefin (PAO) fluid; about 1 wt % or more ofan akylated aromatic fluid; and about 1 wt % or more of an aromaticester; all amounts based on the weight of the blend.
 2. The blend ofclaim 1 comprising: from about 10 wt % to about 98 wt % of a PAO fluid;from about 1 wt % to about 59 wt % of an alkylated aromatic fluid; andfrom about 1 wt % to about 75 wt % of an aromatic ester.
 3. The blend ofclaim 2 wherein the PAO comprise from about 80 to 85 wt %.
 4. The blendof claim 2 wherein the alkylated aromatic comprises about 10 wt %. 5.The blend of claim 2 wherein the ester comprises from about 5 to about 8wt %.
 6. The blend of claim 1 or 2 wherein the alkylated aromatic is analkylated naphthalene having 1 or more alkyl group of from 1 to about 8carbon atoms.
 7. The blend of claim 1 or 3 wherein the aromatic ester isthe product of an aromatic acid or acid anhydride and a straight orbranched aliphatic alcohol of from 3 to 18 carbon atoms.
 8. The ester ofclaim 7 wherein the aromatic acid or anhyride is phthalic acid oranhydride.
 9. A lubricant composition comprising: a major amount of alubricant base stock blend; and an effective amount of at least onelubricant additive selected from the group consisting of antioxidants,rust inhibitors, extreme pressure agents, and metal deactivators; thebase stock blend comprising about 10 wt % or more of a polyalpha olefinfluid; about 1 wt % or more of an alkylated aromatic fluid; and about 1wt % or more of an aromatic ester, the amounts in the blend being basedon the weight of the blend.
 10. The composition of claim 9 wherein theblend comprises: from about 10 wt % to about 98 wt % of a PAO fluid;from about 1 wt % to about 59 wt % of an alkylated aromatic fluid; andfrom about 1 wt % to about 75 wt % of an aromatic ester.